I would be surprised to learn that anyone with significant government experience would believe the Supreme Court is the only branch tasked with considering constitutional questions.
I get this from you: "I would be surprised to learn that anyone with significant government experience would believe the Supreme Court is the only branch tasked with considering constitutional questions."
Ho-kay.... I'll check back later to see if you gave a tad more definitive explanation. Thanks in advance!
Congress is not provided with the authority nor duty to judge whether previous acts of Congress are constitutional. Nor does it provide any member of Congress with the authority to prevent any unstoppable majority of his peers from unconstitional actions. Nonetheless, since any member of Congress has the authority to vote against legislation that is unconstitutional, they have the duty to do so.
Likewise with a president's veto. I don't think anyone would argue that the President has the authority to veto legislation he doesn't like but has some obligation to sign legislation that's unconstitutional. As he is given the authority to veto unconstitional legislation that comes before him, he has the duty to use such authority. Although the Court, unlike the other two branches, has broad powers to strike down legislation which, despite being unconstitional, has previously gotten past the other branches, such power is intended to act only as a 'safety check', and is not intended to be the main means by which the Constitution is upheld.